Under your Account Settings > Email Preferencesyou have the following options related to Watchlist:

Also, if a title is in theatres, on TV, or on Amazon video (and is properly linked into its IMDb title page), that will be indicated on the poster's thumbnail (bottom left corner), and that icon is clickable:

But IMDb does not attempt to keep up with all the streaming services which might offer titles. It's owned by Amazon, and unlike Miracle on 34th Street (1947), Macy's (Amazon) does not tell you at what other stores you can buy (watch) gifts (titles) that Macy's (Amazon) does not carry (stream).